Mu Qing did not sleep.
At his level, not only was he a Xiantian practitioner, but he also possessed the magical artifact bestowed upon him by Master Mingxin, which automatically radiated spiritual energy. Unlike other Xiantian martial artists who needed to leave their bodies and enter the Void Realm to absorb spiritual energy for cultivation, he could simply meditate and contemplate.
Therefore, meditation was all that was required.
Chapter 127